America's number one. Thursday morning. Are canceled today at a high -- sophomore is accused of going on -- slashing and stabbing spree investigators say it started before the day's classes began at a school near Pittsburg more than twenty people are being treated for injuries. And this morning we're learn the learning more about the teen under arrest -- the heroic actions that help stop the attack. ABC -- -- Bradley is live in Marysville Pennsylvania good morning to -- Good morning Diane and John another incident of school violence this high -- actually trains for incidents involving a gunman this time no gun. No one could have imagined that a student would go on a Rampage using knives. Overnight prayers and tears a stunned suburban Pittsburgh community coming together after a shocking act of violence. It happened here at Franklin regional high school yesterday morning. Like -- always need muted here. Police say the sixteen year old sophomore Alex rifle wielding eight to ten inch knives ran through the -- slashing and stabbing anyone he could. 22 people and all -- when students and a security guard. There is glad to right -- -- double doors are all over the wall people running everywhere known knew what to do is if it's a move. New this. Do -- Rival was charged with four counts of attempted homicide and twenty -- counts of aggravated assault. Authorities say he'll be prosecuted as an adult. The FBI removed desktop computers and other items from rivals home the suspect's father offered this message to the victims first. This morning students and faculty are being hailed as heroes. During the attack one wounded student bravely pulled the fire alarm alerting everyone in the building. An assistant principal Sam -- tackled the suspect. Mr. king. And mobilized to meet pinned him down I jumped on top of them as well and just toned down his wrists and arms. Now they're also stories of students rushing to apply pressure to their peers -- Four people remain in critical condition this morning authorities say this could have been so much worse if not for those heroic students and staff. Diana Diana. Bob Bradley live in Marysville Pennsylvania thank you. And student Nate Scania is being credited with saving lives by pulling that fire alarm which forced the school to be evacuated -- was taken along with nineteen others to the hospital after the attacker was subdued. Many -- -- self be with caption -- and at children's and reference to the hospital that he was standing in. And stabbing victims were remembered last night before the penguins red wings game. We expect to learn more as investigators returned to the scene today we'll have live team coverage coming up on Good Morning America.

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